Electrodes of a wide variety of compositions, depending on the application, are provided in gas sensors based on solid electrolytes. Catalytically active electrodes are made of platinum or platinum/rhodium alloys, for example, whereas catalytically inactive electrodes are made of gold or gold alloys. These electrodes are located in internal gas spaces of the sensor, for example, and electrodes of different compositions may be provided in one and the same gas space, depending on the sensor design. Production of such sensors includes at least one high-temperature sintering operation, which may result in contamination of the electrodes with metal constituents of the other electrode. This results in inactivation of catalytically active electrodes due to gold inclusions, for example, or conversely an increased catalytic activity of gold electrodes due to contamination with rhodium or possibly platinum. Both effects negatively impact the sensitive properties of the sensor.
European Published Patent Application No. 678 740 describes a sensor for determining the NOx content of gas mixtures in which electrodes used to monitor the oxygen content within the sensor are made of a gold/platinum alloy, and electrodes for decomposing nitrogen oxides are made of rhodium. Both types of electrodes may be optionally physically separated from one another by a diffusion barrier.
An object of the present invention is to make available a gas sensor for determining the concentration of a component of a gas mixture in which mutual contamination of electrodes is prevented without significantly interfering with access of the gas to be analyzed to the electrodes.